1. Field of the Invention
The present invention essentially comprises an improvement over prior U.S. Pat. No. 4,203,268 issued May 20, 1980, and the present inventors include two of the patentees of the invention covered by such patent.
2. Description of the Prior Art
In the ever present search for ways to minimize cost of producing various objects, savings in the amount and cost of material used therein is a fruitful area to effect savings, especially if quality of the product can be maintained or increased. Constant increases in the cost of steel has given rise to seeking ways to reduce the amount of steel used especially in the access floor panels to which said prior patent primarily pertains.
From an engineering standpoint, when two sheets of steel are attached in parallel but vertically spaced relation to constitute a composite panel unit in which the upper sheet is flat and is subjected primarily to compression, while the lower one is subjected to primarily to tension, the greater the distance between said sheets, the thinner at least the lower tension sheet can be.
In the prior U.S. Pat. No. 4,203,268 such spacing of the compression and tension sheets is effected advantageously by employing circular dome-like projections as shown in FIG. 1A extending upwardly from the bottom tension sheet and welding the uppermost curved section of each dome to the top compression sheet, the projections being arranged in certain advantageous geometric patterns. This arrangement afforded certain advantageous resistance to deflection of the panels due to static or mobile loads, while minimizing the thickness of the sheets to afford acceptable operational requirements and specifications. The search for further savings in materials never ceases, however, and the present applicants know that increasing the depth or space between the compression and tension sheets in the composite structural unit will improve resistance to flexure and thus allow for reductions in material required. It was also known that as the depth of the dome-like projection is increased, the material thins due to stretching and consequently the resistance to crushing is lessened. In addition the applicants know that an optimum shape to resist crushing is a truncated cone as shown in FIG. 1B. It has been discovered, however, that a combination can be provided in the dome-like projections, as illustrated in the aforementioned patent, which provides increased overall depth as well as resistance to crushing. This resistance to crushing can be increased by forming a substantially flat surface on the uppermost peak of the projections of a diameter much less than that of the circular domes.
The truncated cone provides a larger area of support to distribute the load, thus allowing thinning of material due to providing increased depth by stretching without detrimentally affecting the ability of the dome to resist crushing.
The mere use of flat surfaces on the peaks of circular or other shapes of pyramidal type spacing members between parallel structural sheets is old, as shown by the following prior U.S. Patents:
U.S. Pat. No. 2,391,997, Noble, Jan. 1, 1946 PA1 U.S. Pat. No. 3,011,602, Enstrud et al., Dec. 5, 1961 PA1 U.S. Pat. No. 3,025,935, Enstrud, Mar. 20, 1962 PA1 U.S. Pat. No. 3,071,216, Jones et al., Jan. 1, 1963 PA1 U.S. Pat. No. 3,196,763, Rushton, July 27, 1965 PA1 U.S. Pat. No. 3,258,892, Rushton, July 5, 1966 PA1 U.S. Pat. No. 3,527,664, Hale, Sept. 8, 1970 PA1 U.S. Pat. No. 3,876,492, Schott, Apr. 8, 1975
It was found that such use of truncated cone arrangements as employed on the above listed patents greatly limits the height of such cones, even though having flat peak surfaces. Hence, the invention of prior U.S. Pat. No. 4,203,268 was recognized as being patentable over that type of spacing members, due to the use of dome-like projections, especially to resist crushing, together with effective dimensional spacing to minimize the thickness of the sheets and especially the tension sheet.
It has now been discovered by the present applicants that combining the advantages of the depth obtainable by using a dome-like projection, and further including a truncated cone with the flat plane parallel to the original plane of the sheet serves to greatly increase resistance to crushing and provides improved assembly and these improvements also provide a basis for conditions, further effecting a highly desirable increase in the overall height of the projections by structural changes described hereinafter, whereby still further savings may be achieved, in particular, by decreasing the thickness of at least the lower tension sheet.